1. Field of the Invention
The present invention relates broadly to a control valve which allows for the flow control of liquids and gases. More specifically, the invention relates to a control valve which is substantially unsusceptible to plugging and which operates, from a fully open to a fully closed position; relatively noiselessly and free from vibration and cavitation.
2. Description of the Prior Art
Conventional control valves simply utilize an adjustable opening in order to control fluid flows. This adjustable opening may be produced for example in a gate valve or globe valve by adjusting the position of a flat plate, or in a ball valve by adjusting the position of a sphere having an opening passing through it, or in a plug valve or needle valve by adjusting, respectively, a tapered plug or a sharply tapered element. All of such valves are susceptible to severe cavitation with attendant excessive noise levels, vibration and valve wear, particularly at high pressure differentials across the valve.
Other valve designs employ a mixing process wherein fluid flows of different energies are combined, thus producing turbulent fluctuations of a large scale as, for example, the design disclosed in U.S. Pat. No. 3,515,158 (G. E. Utz) which issued on June 2, 1970. Such fluctuations may also produce excessive valve operation noise and vibration. It is important that control valves be smoothly adjustable throughout the range from fully opened to fully closed. An indication of this adjustability for liquid handling valves is the C.sub.v value, wherein C.sub.v is defined as follows: ##EQU1## where Q is the flow rate in gallons per minute, .DELTA. p is the pressure differential in pounds per square inch and .delta. is the specific gravity of the fluid handled. It is particularly important that the C.sub.v vary smoothly as the valve is opened, and that the maximum C.sub.v (fully opened position) is sufficiently large to allow for the passage of an adequate amount of fluid. For many applications, a value with a linear relationship between the valve opening and the flow rate passed through the valve is desired. Thus the flow rate would be zero with the valve closed, and the flow rate would increase substantially in direct proportion to the area of valve opening as the valve is opened. Non-linear valves allow for a large change in flow rate with a rather small change in valve opening; the valve thus not being smoothly adjustable and the control of the flow being more difficult as small changes of valve positions produce wide variations in the flow rate. As the pressure decrease across the valve changes as the valve is opened, the change in pressure drop in turn changes the flow rate. This relationship is governed by the valve characteristics as described by the valve C.sub.v at various openings. Referring to the foregoing formula, the flow rate may be determined when C.sub.v, p and .delta. are determined. While C.sub.v is generally related to liquid handling characteristics, similar term and definition exist for gas flow (often referred to as C.sub.g).
Pressure regulating valves of another design employ a whirl chamber in order to lower the fluid pressure. Such "whirl chamber" valves produce severe underpressures (below the downstream back pressure). Such a pressure differential produces cavitation and/or supersonic downstream gas flow. The cavitation and supersonic flow in turn generate high noise levels. The lowering of allowable noise generation intensity levels by the Federal Occupational Safety and Health administration and numerous state and local agencies typify the long felt need for a control valve capable of operating effectively at low noise levels.
Various means having been suggested to make valves relatively noiseless, but without much success, such as by breaking up the flow of fluid by positioning a disc of fine mesh wire, or a pad of fibrous material, in the fluid-connecting passageway, but such constructions often become plugged due to the small openings in such fibrous materials. Particularly troublesome when handling gaseous fluids are "edge tones" produced by passing the gas over a sharp edge. When the gas flow becomes supersonic, the noise produced by such edge tones is even further increased by as much as an order of magnitude. Additionally, many valve designs have cavities which may act as Helmholtz resonators producing "cavity tones."
Recently developed valving means have successfully utilized a plurality of passages and/or multiple discs in order to make valves relatively noiseless, see for example my U.S. Pat. Nos. 3,133,557 and 3,316,936. However, such valves having a plurality of passages or multiple discs may also become plugged due to the close tolerances within the valves, although to a lesser extent than valves having fine mesh internals.
An object of this invention is to provide a fluid control means which is smoothly adjustable through the operating range from fully opened to fully closed.
An object of this invention is to provide a liquid control valve which is capable of operating without severe cavitation, such cavitation producing excessive noise levels and vibrations.
A further object of this invention is to provide a gas control valve which is capable of operating without severe noise levels and vibration.
An additional object of this invention is to provide for a valve having a design such that underpressures, relative to the downstream back pressure, are not produced thereby generating cavitation with its attendant excessive noise levels and vibration.
A further object of this invention is to provide for a relatively noiseless smoothly operating valve which is not substantially susceptible to clogging by particulate matter.
Further objects and advantages of the present invention will become apparent following a reading of the detailed description, drawings and claims.